Tap-changing transfer switch having series breaks and means for controlling the recovery voltage between breaks

ABSTRACT

A tap-changing transfer switch for tapped regulating transformers is provided with switch means capable of forming series breaks in each of its load current carrying circuits. The transfer switch is further provided in addition to switch-over resistors with resistor means for equalizing the recovery voltage appearing across each of its series breaks. This is achieved without the provision of any auxiliary switching means for switching the voltage distribution resistors.

United States Patent Breuer 'et a].

[4 1 Apr. 16, 1974 TAP-CHANGING TRANSFER SWITCH HAVING SERIES BREAKS AND MEANS FOR CONTROLLING THE RECOVERY VOLTAGE BETWEEN BREAKS Inventors: Wolgang Breuer; Alexander Bleibtreu, both of Regensburg, Germany Assignee: Maschinenfabrik Reinhausen Gebeu der Scheubeck K.G., Rogensburg, Germany Filed: May 31, 1973 Appl. No.: 365,642

Foreign Application Priority Data June 20, 1972 Germany 2230007- U.S. c1. 307/136, 323/415 R rm. Cl. 1101f 29/02 Field of Search 200/11 TC; 307/134, 135, 307/136; 323/435 R; 336/142 [56] References Cited UNITED STATES PATENTS 3,174,097 3/1965 Bleibtreu 307/136 X Primary Examiner--James R. Scott Assistant Examiner-M. Ginsburg Attorney, Agent, or Firm-Erwin Salzer [5 7] ABSTRACT A tap-changing transfer switch for tapped regulating transformers is provided with switch means capable of forming series breaks in each of its load current carry- .ing circuits. The transfer switch is further provided in addition to switch-over resistors with resistor means for equalizing the recovery voltage appearing across each of its series breaks. This is achieved without the provision of any auxiliary switching means for switching the voltage distribution resistors.

2 Claims, 5 Drawing Figures FATENTEBAPR 15 m4 SHEET 2 OF 2 7 FIG! FIGS BACKGROUND OF THE INVENTION This invention refers to tap-changing transfer switches, and more particularly tap-changing transfer switches of the Jansen type which include ohmic tapchanging or change-over resistors which are inserted circuit is continuously derived from one and the same tap of a tapped transformer winding. Tap-changing transfer switches of the aforementioned kind are well known in the art and are described in considerabledetail in U.S. Pat. No. 3,176,089 to A. Bleibtreu et al.,

Mar. 30,1965 for LOAD TAP CHANGERS FOR TRANSFORMERS and reference may be had to this patent for details of transfer'switches in general'which details have no immediate bearing on the present invention.

An invention closely related tothe present invention is disclosed in the. copending patent application Ser.

. A tap changing regulating transformer includes the three following units: (a) a tapped transformer wind- ,ing; (b) a transfer switchproper for switching load currents including overload currents; and (c) a selector switch interposed between the tapped transformer winding and the transfer switch proper for selecting the particular taps to be switched. This invention can be fully, understood without reference to the selector switch circuitry, and a consideration of its presence has, therefore, been deleted from what follows. It may be mentioned, however,thatselector switches and the way in which such switches are associated with a transformer winding and with a transfer switch proper is disclosed in the above referred-to patent to A. Bleibtreu et a]. t

As the voltage of tapped regulating transformers and the power thereof is increased, becomes necessary, or desirable, to substitute in Jansen-type transfer switches for each switching means having a pair of separable contacts, serially arranged switching means capable of forming series breaks when their contacts are separated, or in-the open positions thereof.

Another reason for adopting series-break-forming switching means in Jansen-type transfer switches resides in the fact that the voltage between contiguous tapsof a tapped transformer winding tends to increase in order to cover a relatively large voltage range with a minimum of taps.

The fact that single break contact arrangements must often be replaced by series break contact arrangements gave rise to the problem of controlling the voltage distribution in transfer switches so as to substantially equalize the voltageappearing across each of a plurality of series breaks.

In the past equalization has been achieved by means of special potential control resistors and by utilizing the switch-over resistors of transfer switches for voltage distribution purposes. Prior art transfer switches involving potential controls for series breaks require separate or additional control switches for establishing the into the load circuit during tap-changing operations, but are not inserted into the load circuit when the load required potential control circuits. This is a very serious drawback because these switches greatly increase the bulk and the complexity of the transfer switch proper, and require additional operating means, and means for timing their operation. In addition thereto such separate or additional control switches must be designed to withstand the high voltages present in transfer switches of the kind under consideration.

It is the primary object of this invention to provide transfer switches for tap-changing transformers wherein each path of the load current is provided with switching means, or separable contact means, forming series breaks upon opening thereof, wherein the voltage across all these breaks is controlled in such a fashion that the voltage across each of a plurality of series breaks is substantially equal, and wherein these ends are achieved without resorting to separate or additional voltage control switches which must be opened and No. 365,643 filed May 31, 1973 of Wolfgang Breuer et closed in predetermined sequences.

SUMMARY OF THE INVENTION Transfer switches embodying this invention include means establishing a first load current branch extending from a first transformer winding tap to a load, and means establishing a second load current branch extending from a second transformer winding tap to said load.

Each said first load current branch and said second load current branch include a main current path and an auxiliary current path parallel to said main current path. Said main current path and said auxiliary current path of each said first and second load current branch are provided with at least two serially arranged switch means having relatively'movable contacts forming series'breaks inthe open positions thereof. The auxiliary current path of said first and said second load current branch each includea tap-changing or switch-over resistor. The switch-over resistorof said first load current branch is inserted betweenthe tap end of saidfirst load current branch and said switch means of the auxiliary current path thereof. The switch-over resistor of said second load current branch is inserted between thetap end of said second load current branch and said switch means in the auxiliary current path thereof.

Transfer switches embodying this invention further include a pair of potential control resistors for controlling the potential distribution in said main current path of said first and said second load current branch. Each of said pair of potential control resistors conductively interconnects one point situated between the two ends of said switch-over resistor of said first and second load current branch with one point situated between two of said serially arranged switch means in said main current path of said first and second load current branch.

Transfer switches embodying this invention further include an additional pair of potential control resistors for controlling the potential distribution in said auxiliary current path of said first and second load current branch. One of said pair of additional potential control resistors conductively interconnects the tap end of said first load current branch with a point of said auxiliary current path of said second load current branch situated between said switch means thereof. The other of said pair of additional potential control resistors conductively interconnects the tap end of said second load current branch with a point of said auxiliary current path of said first load current branch situated between said switch means thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic representation of a tapchanging transfer switch embodying the present invention, FIG. 1 showing the switch in one of its two limit positions;

FIG. 2 shows the same switch as FIG. 1 and in the same fashion as FIG. 1 and shows the constituent parts thereof in a first intermediate position between its two limit positions;

FIG. 3 shows the same switch in FIG. 1 in the same fashion as FIG. 1 and shows the constituent parts thereof in a second intermediate position between its two limit positions;

FIG. 4 shows the same switch as FIG. 1 in the same fashion as FIG. 1 and shows the constituent parts thereof in a third intermediate position between its two limit positions; and

FIG. 5 shows the same switch as FIG. 1 in the same fashion as FIG. 1 and shows the constituent parts thereof in the other of its two limit positions.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, reference characters U, and U have been applied to indicate two contiguous taps of a tapped transformer winding. In the first stationary or limit position of the transfer switch shown in FIG. 1 the load current derived from tap U, flows from that tap by way of load current branch L, to a load not shown. In the second stationary or limit position of the transfer switch the load current is derived from tap U and flows from that tap by way of load current branch L, to a load not shown. Load current branch L, includes the main current path I and the auxiliary current path III arranged parallel to the main current path I. In a like fashion load current branch L includes the main current path II and the auxiliary current path IV arranged parallel to the main current path II. The main current path I is provided with at least two serially conpositions thereof. In like fashion the main current path 'II of current branch L, is provided with at least two sein the open positions thereof. The auxiliary current path III is provided with at least two serially connected auxiliary switch means III, and III, having relatively movable contacts and forming series breaks in the open position thereof. In like fashion the auxiliary current path IV is provided with at least two serially connected auxiliary switch means IV, and IV, having relatively movable contacts and forming series breaks in the open positions thereof. Reference characters R, and R, have been applied to indicate a pair of switch-over resistors, or tap-changing resistors, which are inserted into the load circuit when performing a tap-changing operation from tap U, to tap U,, or from tap U, to tap U,. Resistor R, is inserted between tap U, and switch means III,, III,

and resistor R, is inserted between tap U, and switch means IV,, 1V Resistor R, is subdivided into two seri-' ally connected resistor portions R,, and R,, and a tap is formed between the two resistor portions R,, and R,,. In like fashion switch-over or tap-changing resistor R, is subdivided into two resistor portions R,,, and R,,, and

' nected main switch means I, and I, having relatively movable contacts and forming series breaks in the open a tap is formed between resistor portions R,, and R,,. The tap formed between resistor portions R,, and R,, is conductively connected by means of potential control resistor R, to a point of main current path I situated between switch means I, and I In like fashion the tap formed between resistor portions R,, and R is conductively connected by means of potential control resistor R to a point of main current path II situated between switch means II, and II,. Reference characters R,,, and R,,, have been applied to indicate an additional pair of potential control resistors. These resistors R R are provided for controlling the potential distribution in auxiliary current paths III and IV. Resistor R,,, conductively interconnects a point between switch means III, and III 2 and tap U Resistor R conductively interconnects a point between switch means IV, and IV, and tap U,.

Switch means I, and I, are supposed to open and to close simultaneously, and to this end they may be tied together mechanically as indicated in the drawings by a dotted line. The same applies as to the pairs of switch means III,, III, and to the pair of switch means IV,, IV, and to the pair of switch means II,, II,. This has also been indicated in the drawings by dotted lines interconnecting switch means that open and close simultaneously.

In the position of parts shown in FIG. 1 the entire load current is derived from tap U, and flows through first current branch L, and the two serially connected switch means or switches I, and I, arranged in main current path I. Switch means III,, III,; IV,,IV and R,,", are open and, therefore, no current flows through auxiliary current paths III and IV and through main current path II.

. The first step in performing a tap-changing operation from tap U, to tapU, consists in simultaneously closing auxiliary switch means III, and III, in auxiliary current path III and shortly thereafter simultaneously opening main switch means I, and I, in main current path I. This position of parts is shown in FIG. 2. Closing of switch means III, and III, results in a voltage drop across resistor R,. That voltage drop is used along with the voltage drop along potential control resistor R, for controlling or equalizing the potential across main switch means I, and 1,. When the latter switch means open an arc may be formed across each of the resulting breaks, but such arcs extinguish at the first current zero. Now the entire load current is carried by auxiliary current path III and auxiliary'switches III, and Ill and the current is then limited by the insertion of switch-over resistor R, into the aforementioned current path. In order to equalize the voltage across the series breaks formed by the opening switching devices I, and I, the sections R,, and R,, into which resistor R, is sub-divided must be of equal magnitude.

The next step in performing a tap-changing operation from tap U, to tap U, consists in closing the two auxiliary switch means IV, and IV, in auxiliary current path IV, resulting in the position of parts shown in FIG. 3. In that position there is, in addition to the flow of the load current to the load not shown a flow of a circulating current from tap U, through registor R, and switch means III, and III, and resistor R, and switch means IV, and IV, to tap U The magnitude of that circulating current is limited by the sum of resistors R, and R,. In addition to the above circulating current there are two other circulating currents whose paths extend from tap U through Resistor R and from tap U through resistor R These circulating currents are minimal on account of the magnitude or high ohmic value of resistors R and R The next step in performing a tap-changing operation from tap U to tap U consists in interrupting the auxiliary current path III by simultaneously opening switch means Ill, and lll This results in the position of parts shown in FIG. 4. Forming of breaks at Ill and H1 may result in the formation of arcs at these breaks, but these arcs are short-lived and extinguish at the first current zero. When the switch means III and Tll open, a recovery voltage appears across the separated contacts thereof. The recovery voltage across the separated contacts of switch means llll, corresponds to the voltage drop across switch-over resistor R The magnitude switch-over resistor R may be determined in such a way that the voltage drop along switch-over resistor R is equal to the voltage normally prevailing between contiguous taps U and U The recovery voltage appearing across the separated contacts of switch means lll is equal to the difference in potential between taps U and U since the voltage of tap U is' applied by means of resistor R to the point between switches III, and 111 Hence the recovery voltage is evenly distributed across the two breaks formed by auxiliary switch means III and lli I The next step in performing a tap-changing operation from tap U to tap U consists in simultaneously closing the main contact means Ill and ll This establishes'a direct current path from tap U, to the load (not shown). Thereafter auxiliary switch means IV, and W are opened simultaneously. No arcing occurs when these switchmeans are opened since the current path II forms a very low resistance shunt across the current path IV. Opening of contact means IV and 1V terminates the tap-changing operation from tap U, to tap U The second limit position of the transfer switch when the entire load current is derived only from tap U is shown in FIG. 5.

It will be noted from the above that the transfer switch does notrequire any additional switch means for the control of the recovery voltage across its four pairs of switch means I, and 1 II, and ll lll and Illand IV, and W i.e. it does not require any additional switch means for switching either of the potential control resistors R R and R R The tap-changing operation from tap U to tap U does not need to be described specifically since the consecutive steps involved in this operation are apparent from what has been described above. Suffice it to this invention further include two pairs of jointly movable main switch means 1,, I and llhllg having relatively movable contacts. One pair I,,I of said two pairs of main switch means l l ll ll is arranged in series in said main current path I of said first load current branch L and forms series breaks in the open positions thereof; The other pair ll ll of said main switch means is arranged in series in the main current path II of said second load current branch L and forms series breaks in the open positions thereof. Systems embodying this invention further include two pairs of jointly movable auxiliary switch means lll lll and IV lV having relatively movable contacts. One pair III,,III of said two pairs of auxiliary switch means lll lll IV IV is arranged in series in said auxiliary current path III of said first load current branch L, and forms series breaks in the open positions thereof. The other pair IV,,IV of said two pairs of auxiliary switch means lll lll and l-V,,IV is arranged in series in the auxiliary current path IV of said second load current branch L and forms series breaks in the open positions thereof.

Systems embodying this invention further include a pair of switch-over resistors R R One of said pair of switch-over or tap-changing resistors R R is interposed between said first tap U and auxiliary switch means lll lll The other switch-over or tap-changing resistor R is interposed between tap U and switch means IV ,lV

Systems embodying this invention further include a pair of potential control resistors R ,R for controlling the potential distribution in said main current path I of said-first load current branch L, and in said main current path ll of said second load current branch L One of said pair of potential control resistors R R interconnectsconductively one point situated between the ends of switch-over resistor R, with a point situated between main switch means I, and I The other of said pair of potential control resistors R 11 conductively interconnects one point situated between the ends of switch-over resistor R, with a point situated between main switch means Il and IE Systems embodying this invention further include an for controlling the potential distribution in'said auxiliary current path III of the first load current branch L,

- tential control resistors conductively interconnects the say that when switching means IV, and W are opened simultaneously the voltage control in auxiliary current path IV is effected by resistor R of which one end is connected to tap U and the other to a point situated between switching means TV, and W It will be apparent from the above that systems embodying the present invention include a tapped transformer winding having a first tap U and a contiguous second tap [1,. Such systems further include a first load current branch L, for conductively connecting said first tap U to aload, and a second load current branch L, for conductively connecting said second tap U to a load. Each said first load current branch L, and said second load current branch L, include a main current path I and II, and an auxiliary current path III and IV parallel to said main current path. Systems embodying first tap U, with a point situated between auxiliary switch means IV; and W The other of said additional pair of potential control resistors conductively interconnects the second tap U, with a point situated between auxiliary switch means lll and lll We claim as our invention:

1. A tap-changing transfer switch for tapped transformer windings having series breaks and means for controlling the recovery voltage between breaks comprising in combination a. means establishing a first load current branch from a first transformer tap to a load;

b. means establishing a second load current branch from a second transformer winding tap to said lead;

c. each said first load current branch and said second load current branch including a main current path and an auxiliary current path parallel to said main current path, each said main current path and said auxiliary current path being provided with at least two serially arranged switch means having relatively movable contacts forming series breaks in the open positions thereof, and said auxiliary current path of said first and second load current branch each including a switch-over resistor, said switch-over resistor of said first load current branch being inserted between the tap end of said first load current branch and said switch means of the auxiliary current path thereof, and said switchover resistor of said second load current branch being inserted between the tap end of said second load current branch and said switch meansin the auxiliary current-path thereof;

(1. a pair of potential control resistors for controlling the potential distribution in said main current path of said first and said second load current branch, each of said pair of potential control resistors conductively interconnecting one point situated between the two ends of said switch-over resistor of said first and second load current branch with one point situated between two of said serially arranged switch means in said main current path of said first and second load current branch; and

e. an additional pair of potential control resistors for controlling the potential distribution in said auxiliary current path of said first and second load current branch, one of said pair of additional potential control resistors conductively connecting the tap end of said first load current branch with a point of the auxiliary current path of said second load'current branch situated between said swith means thereof, and the other of said pair of additional potential control resistors conductively connecting the tap end of said second load current branch with a point of the auxiliary current path of said'tirst load current branch situated between said switch means thereof.

- 2. In combination I v a. a tapped transformer winding having a first tap and a contiguous second tap;

b. a first load current branch for conductively conseries in said main current path of said first load current branch and forming series breaks in the open positions thereof and the other pair of said two pairs of main switch means being arranged in series in the main current path of said second load current branch and forming series breaks in the open positions thereof;

. two pairs of jointly movable auxiliary switch means having relatively movable contacts, one pair of said two pairs of auxiliary switch means being arranged in series in said auxiliary current path of said first load current branch and forming series breaks in the open positions thereof and the other pair of said two pairs of auxiliary switch means being arranged in series in the auxiliary current path of said second load current branch and forming series breaks in the open positions thereof; a pair of switch-over resistors, one of said pair of switch-over resistors being interposed between said first tap and said one pair of auxiliary switch means and the other of said pair of switch-over resistors being interposed between said second tap and said other pair of auxiliary switch means;

g. a pair of potential control resistors for controlling the potential distribution in said main current path of said first load current branch and in said main current path of said second load current branch, one of said pair of potential control resistors conductively interconnecting one point situated between the ends of said one of said pair of switchover resistors with one point situated between said one pair of said two pairs of main switch means and the other of said pair of potential control resistors conductively interconnecting one point situated between the ends of said other of said pair of switch-over resistors with one point situated between said other pair of said two pairs of main switch means; and

h. an additional pair of potential control resistors for controlling the potential distribution in said auxiliary current path of said first load current branch and in said auxiliary current path of said second load current branch, one of said additional pair of potential control resistors conductively interconnecting said first tap with a point situated between said other pair of said two pairs of auxiliary switch means and the other of said additional pair of potential control resistors conductively interconnecting said second tap with a point situated between said one pair of saidtwo pairs of auxiliary switch means. 

1. A tap-changing transfer switch for tapped transformer windings having series breaks and means for controlling the recovery voltage between breaks comprising in combination a. means establishing a first load current branch from a first transformer tap to a load; b. means establishing a second load current branch from a second transformer winding tap to said load; c. each said first load current branch and said second load current branch including a main current path and an auxiliary current path parallel to said main current path, each said main current path and said auxiliary current path being provided with at least two serially arranged switch means having relatively movable contacts forming series breaks in the open positions thereof, and said auxiliary current path of said first and second load current branch each including a switchover resistor, said switch-over resistor of said first load current branch being inserted between the tap end of said first load Current branch and said switch means of the auxiliary current path thereof, and said switch-over resistor of said second load current branch being inserted between the tap end of said second load current branch and said switch means in the auxiliary current path thereof; d. a pair of potential control resistors for controlling the potential distribution in said main current path of said first and said second load current branch, each of said pair of potential control resistors conductively interconnecting one point situated between the two ends of said switch-over resistor of said first and second load current branch with one point situated between two of said serially arranged switch means in said main current path of said first and second load current branch; and e. an additional pair of potential control resistors for controlling the potential distribution in said auxiliary current path of said first and second load current branch, one of said pair of additional potential control resistors conductively connecting the tap end of said first load current branch with a point of the auxiliary current path of said second load current branch situated between said swith means thereof, and the other of said pair of additional potential control resistors conductively connecting the tap end of said second load current branch with a point of the auxiliary current path of said first load current branch situated between said switch means thereof.
 2. In combination a. a tapped transformer winding having a first tap and a contiguous second tap; b. a first load current branch for conductively connecting said first tap to a load, and a second load current branch for conductively connecting said second tap to said load; c. each said first load current branch and said second load current branch including a main current path and an auxiliary current path parallel to said main current path; d. two pairs of jointly movable main switch means having relatively movable contacts, one pair of said two pairs of main switch means being arranged in series in said main current path of said first load current branch and forming series breaks in the open positions thereof and the other pair of said two pairs of main switch means being arranged in series in the main current path of said second load current branch and forming series breaks in the open positions thereof; e. two pairs of jointly movable auxiliary switch means having relatively movable contacts, one pair of said two pairs of auxiliary switch means being arranged in series in said auxiliary current path of said first load current branch and forming series breaks in the open positions thereof and the other pair of said two pairs of auxiliary switch means being arranged in series in the auxiliary current path of said second load current branch and forming series breaks in the open positions thereof; f. a pair of switch-over resistors, one of said pair of switch-over resistors being interposed between said first tap and said one pair of auxiliary switch means and the other of said pair of switch-over resistors being interposed between said second tap and said other pair of auxiliary switch means; g. a pair of potential control resistors for controlling the potential distribution in said main current path of said first load current branch and in said main current path of said second load current branch, one of said pair of potential control resistors conductively interconnecting one point situated between the ends of said one of said pair of switch-over resistors with one point situated between said one pair of said two pairs of main switch means and the other of said pair of potential control resistors conductively interconnecting one point situated between the ends of said other of said pair of switch-over resistors with one point situated between said other pair of said two pairs of main switch means; and h. an additional pair of potential control resistors for controlling the potential distribution In said auxiliary current path of said first load current branch and in said auxiliary current path of said second load current branch, one of said additional pair of potential control resistors conductively interconnecting said first tap with a point situated between said other pair of said two pairs of auxiliary switch means and the other of said additional pair of potential control resistors conductively interconnecting said second tap with a point situated between said one pair of said two pairs of auxiliary switch means. 